1. Field of the Invention
The present application relates to a liquid crystal display device, and more particularly, to a driving system for a liquid crystal display device including a liquid crystal panel and a backlight unit, a liquid crystal display device including the driving system, and a driving method using the driving system.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices having thin profiles, light weight, and low power consumption have been used in notebook computers, office automation devices, audio/video devices, and the like. Among the various types of LCD devices, active matrix LCD (AM-LCD) devices that employ switching elements and pixel electrodes arranged in a matrix structure are the subject of significant research and development because of their high resolution and superior suitability for displaying moving images. Thin film transistor LCD (TFT-LCD) devices use thin film transistors (TFTs) as the switching elements.
FIG. 1 is a view showing a liquid crystal display device according to the related art. In FIG. 1, the LCD device includes a liquid crystal panel 10, a backlight unit 20, a control unit 30, a system unit 40, and an inverter unit 50. The liquid crystal panel 10 includes a plurality of pixels to display images corresponding to applied data signals, and the backlight unit 20 includes an illuminating means to supply light to the liquid crystal panel 10. The control unit 30 includes a timing controller to control display of the images via the data signals supplied to the liquid crystal panel 10. The system unit 40 includes an external interface circuit, such as a television system or a graphic card, to supply image data corresponding to the data signals and various driving signals to the control unit 30. In addition, the inverter unit 50 controls illumination of the backlight unit 20 and receives a dimming signal for adjusting illumination of the backlight unit 20 from the control unit 30 or the system unit 40.
Recently, a driving method of an LCD device that improves contrast ratio has been suggested. In the driving method, contrast ratio is improved by reducing luminance of the backlight unit for images within a low gray level range, specifically an image corresponding to black. Accordingly, display quality is improved while reducing power consumption. For example, the image data within the low gray level range may be converted to have a higher gray level and the luminance of the backlight unit may be reduced.
FIG. 2 is a view showing a driving system for improving contrast ratio for a liquid crystal display device according to the related art. In FIG. 2, the driving system includes a control unit 30, a system unit 40, and an inverter unit 50. The system unit 40 supplies dimming signals to the inverter unit 50 through a second cable CB2 connecting a first system connector 44 and a first inverter connector 52. The dimming signals may be classified into A and B types. The A type dimming signal is an analog direct current (DC) voltage signal while the B type dimming signal is one of a pulse width modulation (PWM) signal and an analog DC voltage signal. Accordingly, the system unit 40 supplies a first B type dimming signal VBR-B1 to the control unit 30 through a first cable CB1 connecting a second system connector 42 and a first control connector 34.
When the system unit 40 supplies a dynamic contrast ratio (DCR) enable signal DCR-EN to the control unit 30, a timing controller 32 of the control unit 30 generates a timing controller dimming signal DACOUT of an analog DC voltage signal corresponding to the data signal. One of the first B type dimming signal VBR-B1 supplied from the system unit 40 and the timing controller dimming signal DACOUT generated by the timing controller 32 is selected through a first multiplexer M1 of the control unit 30. The control unit 30 supplies the selected dimming signal as a second B type dimming signal VBR-B2 to the system unit 40 through the first cable CB1.
One of the first and second B type dimming signals VBR-B1 and VBR-B2 is selected through a second multiplexer M2 in the system unit 40. The system unit 40 supplies an A type dimming signal VBR-A and the selected dimming signal as a B type dimming signal VBR-B to the inverter unit 50 through the second cable CB2 connecting the first system connector 44 and the first inverter connector 52. The inverter unit 50 adjusts luminance and lighting period of the backlight unit of the LCD device using the A and B type dimming signals VBR-A and VBR-B.
Accordingly, the control unit 30 selects one of the timing controller dimming signal DACOUT generated by the control unit 30 and the first B type dimming signal VBR-B1 supplied by the system unit 40 as the second B type dimming signal VBR-B2. The selected dimming signal (i.e., DACOUT or VBR-B1) is supplied as the second B type dimming signal VBR-B2 to the system unit 40. The system unit 40 then selects one of the first B type dimming signal VBR-B1 generated by the system unit 40 and the second B type dimming signal VBR-B2 supplied by the control unit 30 as the B type dimming signal VBR-B. The A type dimming signal VBR-A and the B type dimming signal VBR-B are supplied to the inverter unit 50.
Since the DCR enable signal DCR-EN, the first type dimming signal VBR-B1, and the second B type dimming signal VBR-B2 are transmitted between the system unit 40 and the control unit 30, additional transmission lines are required in the first cable CB1. As a result, additional pins are required in the first control connector 34 and the second system connector 42, and a general system unit is not applicable to the driving method for improving contrast ratio. For example, a number of pins of the first control connector 34 for the contrast ratio improvement driving method may be greater than a number of pins of a second system connector of the general system unit. Since at least three pins for the DCR enable signal DCR-EN, the first type dimming signal VBR-B1, and the second B type dimming signal VBR-B2 are required in the second system connector of the general system unit, changes in the pin map of the second system connector is required to accommodate the additional pins.